The invention relates to a transponder provided with an integrated circuit, an antenna, and a first capacitor provided with a dielectric and a first and a second capacitor electrode, which transponder comprises a stack of layers, i.e.:
a first layer of a dielectric material,
a first patterned electrically conductive layer of which the antenna forms part,
a second layer of a dielectric material, and
a second patterned electrically conductive layer.
The invention further relates to an appliance provided with a transponder which comprises an integrated circuit, an antenna, and a first capacitor.
Such a transponder is known from EP-A-840251. The second layer of dielectric material in the known transponder is the dielectric of the capacitor and at the same time the substrate. The transponder comprises an electrically conductive connection which is passed through the second layer of dielectric material. This connection is present in the form of a metal-filled hole in the second layer. The integrated circuitxe2x80x94also referred to hereinafter as ICxe2x80x94of the known transponder is separately manufactured and is provided on the second patterned layer in an assembling step. To protect the second patterned layer and the IC, the known transponder comprises a top layer of dielectric material. The antenna of the known transponder is present in the first patterned layer which is manufactured separately from the second patterned layer on the first layer of dielectric material. The two halves of the transponder are subsequently assembled together.
A disadvantage of the known transponder is that its cost price is high, as an assembling step of the IC is necessary.
It is a first object of the invention to provide a transponder of the kind described in the opening paragraph which can be manufactured at a low cost price. A second object of the invention is to provide an appliance of the kind mentioned in the second paragraph which comprises a transponder which can be integrated in the appliance in a simple manner.
The first object is achieved in that the second patterned layer comprises a first electrode of the integrated circuit and the second capacitor electrode.
The second patterned layer does not only comprise the second capacitor electrode, as in the cited application, but also the first electrode of the IC. Instead of assembling an IC, the IC is processed onto the second layer or a further layer of dielectric material. An additional advantage of said processed IC is that bonding problems are absent. Such problems include a bad electrical connection, a bad adhesion to the second layer of dielectric material. Further on, the flexibility of the IC is enhanced in that a processed IC can be flexible whereas an assembled IC is not. Another advantage is that in the design the condition of ease of assemblage of the IC is absent. This condition being absent, the design can be optimized to have large capacitor electrodes and large contact surfaces, if present. In the case that in the manufacture of the transponder two halves are processed independently and assembled during a later step, the large size of electrodes and contact surfaces facilitates an easy assembly of both halves.
The processed IC further comprises other parts such as a semiconductor and a second electrode. These parts may be present in the form of doped regions in a layer of a semiconducting material such as silicon. The IC may alternatively comprise a layered structure. The first electrode of the IC may form part of a first transistor or of a first diode. Preferably, the IC comprises several transistors as well as interconnect lines between the transistors. Said interconnect lines can be present in the second patterned electrically conductive layer. Preferably, the IC further comprises one or several memory elements.
It is advantageous that the second layer of dielectric material is the dielectric of the first capacitor and comprises a first interconnection between the antenna and the integrated circuit. In this case, the second layer of dielectric material is not only the dielectric of the first capacitor, but it also has the functions of an insulator between and of a protective layer for the first and the second patterned layer. Preferably, the dielectric material of the second layer has a relative dielectric constant ∈xcfx84 of approximately 3 to 30. A semiconducting layer may be in contact with the layer of dielectric material. Preferably, the semiconducting layer is thinner than the second layer of dielectric material.
By preference, the first patterned layer comprises not only the antenna, but also the first capacitor electrode. This layer may in addition comprise a first contact surface which is in contact with or forms part of a first connection. Preferably, the integrated circuit is connected to the antenna by means of this first interconnection.
There are various embodiments of the transponder according to the invention which differ from one another in the nature of the interconnection between the antenna and the IC. The number of connections is at least two, because the antenna and IC form part of a closed electric circuit. In a first embodiment, there is a connection between the first and the second patterned layer through the second layer of dielectric material, which second layer is patterned. There are various methods for the manufacture of a hole in the second layer which is then to be filledxe2x80x94a connection which is known to those skilled in the art as a vertical interconnect area or viaxe2x80x94, for example, a mechanical and a photochemical method.
In a second embodiment, there is an interconnection between the first and the second patterned layer which extends outside the layer of dielectric material. This embodiment has the advantage that no through hole need be filled, which would be an additional step in the manufacture. In a third embodiment, there is a connection at the outside of the transponder. Such a connection comprises roughly a U-shaped part.
In a fourth, favorable embodiment of the transponder, the first capacitor constitutes the interconnection. A first advantage of the use of capacitors as interconnect members is that this saves a patterning of the second layer of dielectric material. A second advantage is that no problems can arise as regards positioning of the second patterned layer with respect to the first.
The antenna in the transponder according to the invention serves for communication with a base station. At least three techniques are known by which such a communication can take place. The first technique is inductive coupling, where the communication takes place magnetically. When this technique is used, a coil is present in the pattern of the first layer on the transponder, and a capacitor is present in a tuned circuit. The second technique is capacitive coupling, where the communication takes place electrically. In this case, two capacitor plates are present on the transponder, which plates communicate with one or several capacitor plates in the base station. A diode is further present in the tuned circuit. The third technique makes use of radiation, i.e. communication takes place by electromagnetic means.
The integrated circuit in the transponder according to the invention is present in an electric circuit which is usually operated with direct current. Since the tuned circuit is usually operated with alternating current, a diode and a capacitor will mostly be present in the current path of the integrated circuit. Preferably, the diode is integrated into the IC. The diode may be present in the form of a field effect transistor provided with a gate, a source, and a drain electrode, the gate electrode being short-circuited with the source or drain electrode. The capacitor referred to above has a smoothing function. Said capacitor may be integrated into the IC, the dielectric between the gate electrode and the semiconducting layer being at the same time the dielectric of this capacitor. Said capacitor may alternatively be integrated into the layer structure of the first patterned layer, the second dielectric layer, and the second patterned layer.
Capacitors in the transponder according to the invention accordingly serve to fulfill at least one of the following functions: smoothing the signal supplied by the diode; providing resonance if the antenna is a coil; interconnecting the antenna and the integrated circuit; and providing a capacitive coupling to a base station. Although the capacitors will be different from an electrical point of view in dependence on these functions, they are comparable from a physical point of view.
It is preferable for all capacitors present to be integrated into the layer structure which is formed by the first patterned electrically conductive layer, the second layer of dielectric material, and the second patterned electrically conductive layer. Interference with the integrated circuit by the capacitors is thereby prevented. This is true in particular if polymeric materials are used for one or several layers with conductive patterns and for the semiconducting layer. Interference with the integrated circuit by parasitic capacitors is much stronger with the use of such materials than with the use of conventional integrated circuits based on silicon.
It is realized in a favorable embodiment that
the first patterned layer comprises the first and a third capacitor electrode,
the second patterned layer comprises a fourth capacitor electrode,
the third and the fourth capacitor electrode form a second capacitor in conjunction with the second layer of dielectric material,
the first capacitor forms the first connection between the integrated circuit and the antenna, and
the second capacitor forms a second connection between the antenna and the integrated circuit.
In this embodiment, the first and the third capacitor electrode preferably form the antenna of the transponder, which antenna receives power and transmits signals through capacitive coupling to a base station during operation. The capacitor electrodes at the same time form part of the connections between the antenna and the integrated circuit. The second layer of dielectric material is the dielectric of both the first and the second capacitor, and preferably also the substrate for the second layer. Since these layers of the transponder have a dual function, the number of components of the transponder is comparatively small. The cost price of the transponder is comparatively low as a result. A stack comprising a semiconducting layer, a dielectric, and a third layer may additionally be present on the second patterned electrically conductive layer. The presence of these layers is dependent on the type of integrated circuit which is used in the transponder.
In a special embodiment, the first patterned layer occupies a larger surface area than does the second patterned layer. Preferably, the first layer of dielectric material forms the substrate for the first patterned layer, and the second layer of dielectric material forms the substrate for the second patterned layer, while the first layer of dielectric material has a larger surface area than the second layer of dielectric material. In this embodiment, the surface of the second patterned layer in which the first electrode of the integrated circuit is provided has comparatively small dimensions. The number of integrated circuits with capacitor electrodes which can be manufactured on one wafer is accordingly great. This is important for the cost price both in the case of an integrated circuit based on silicon and in the case of an organic integrated circuit. The size of the first patterned layer on the other hand may lie within wide limits. This has the advantage that the range of the antenna is not limited by the size of the second patterned layer.
In a further embodiment, the integrated circuit has a layered structure. The IC in this embodiment has a second electrode, while
a stack of a semiconducting layer, a third layer of dielectric material, and a third patterned electrically conductive layer comprising the second electrode of the integrated circuit is present on the second patterned layer, and
a fourth layer of dielectric material is present on said stack.
The integrated circuit is provided in the second patterned layer and the stack. This IC comprises a first transistor with inter alia a source, a drain, and a gate electrode, the source and drain electrodes lying in the same patterned layer and the gate electrode lying in a different patterned layer. The integrated circuit preferably further comprises a first memory element and electrical conductors for the interconnection of elements in the circuit such as the first transistor and the first memory element. The stack may be built up in the order: semiconducting layer, third layer of dielectric material, and third patterned layer. An alternative sequence is also possible: third layer of dielectric material, semiconducting layer, and third patterned layer. The further sequence is possible: third layer of dielectric material, third patterned layer, and semiconducting layer.
A first advantage of this embodiment is that it can be manufactured in a simple manner. The fourth layer of dielectric material may be used as a second substrate, while the first layer of dielectric material is used as the first substrate. Both substrates may thus be provided with a patterned layer independently of one another. This is favorable because the dimensions of the patterns in the first and in the second patterned layer are usually strongly different. The transponder is obtained by assembling the two substrates together. Preferably, the first and the fourth layer of dielectric material for this purpose have a larger surface area than the patterned layer deposited thereon, so that end portions of the first and the fourth layer are exposed. These end portions are in contact with one another and fixed together after being assembled.
A second advantage of the embodiment with a fourth layer of dielectric material is the possibility of a connection between the IC and the antenna through contact surfaces laterally of the second layer of dielectric material. It is possible to obtain a via without a hole in the second layer of dielectric material having to be filled with electrically conductive material. This saves one process step. In addition, the connection thus obtained is very robust because a large contact surface area is present between the contact surfaces which form part of the first and the second patterned layer.
A third advantage of the embodiment of the transponder according to the invention is that the first and the fourth layer of dielectric material may be laminated together, so that a substantially uninterrupted protective layer is present. The protective layer provides protection against damage which could arise from chemical, electrical, or mechanical causes. This layer need not be provided in an additional step, which reduces the cost price as well as the thickness of the transponder.
In a favorable embodiment, at least one of the layers comprises mainly organic material. An IC having one or several layers of organic material has a comparatively low cost price on account of low material costs and because large numbers of the IC can be manufactured in one batch. A layer of organic material can be provided on a substrate in a simple manner by a coating technique, such as web coating or spin coating. A number of materials have been described for which it is possible to pattern the provided layer subsequently without necessarily using an etching mask. Examples are inter alia polyanilines, photoresists, and polythiophenes in combination with polyacids. A transponder which is composed entirely or partly from organic materials has a comparatively low mass and a comparatively small thickness. This is advantageous if the transponder according to the invention is used as an indetachable component of a variety of appliances such as paper money and other valuable papers, packagings, and toys. The first layer of dielectric material, which is coated with the first patterned layer on its upper surface, may be provided with a glue layer on its bottom surface.
Preferably, a semiconducting layer of organic material is used. This semiconducting material has the advantage that no separate doping need be provided. In addition, the material can be provided in a simple manner by spin or web coating. Examples of semiconducting organic materials are pentacene, polythiophene, polythienylene-vinylene, polyphenylene-vinylene, polyfuranylene-vinylene, polypyrrole, polyacetylene, polyfurane, and polyaniline. Substituted variants of these materials may alternatively be used. Examples of substituents are alkyl, alkoxy, and alkylalkoxy groups and ring-shaped groups such as alkylenedioxy groups. Such groups are preferably C1 to C10-alkyl, -alkoxy, or -alkylenedioxy.
It is furthermore advantageous when at least one of the patterned layers comprises a doped organic polymeric material. Preferably, the second and the third patterned layer comprise organic polymeric material. Advantages of this are inter alia the cost saving and the flexibility of the material. Furthermore, a layer of doped organic polymeric material can be provided in a simple manner and patterned on a flexible substrate. It is preferable that a patterned layer of organic material forms a relief, the electrically non-conducting regions of the layer being removed. Examples of organic materials which may be used after doping as electrically conductive materials are inter alia polyaniline, polythiophene, poly(p-phenylene sulfide), and copolymers of these materials. Other useful materials are substituted variants of the above materials. Examples of substituents are alkyl, alkoxy, and alkylalkoxy groups and ring-shaped groups. Particular examples are poly-3-alkylthiophenes, poly-3,4-dialkoxythiophenes, poly-3,4-alkylthiophenes, and poly-3,4-alkylenedioxythiophenes. Such substituted groups are preferably C1 to C10-alkyl, alkoxy, or alkylenedioxy.
Other examples of electrically conductive materials which can be used in the patterned electrically conductive layers are gold, copper, TiN, TiW, doped silicon, aluminum, cobalt, titanium and other metals and alloys. Examples of materials which can be used in the first, second and fourth layers of dielectric material, include polyimide, polyethylene terephthalate (PET) and paper. Layers of such a material can act as a substrate of a transponder very well.
The second object of the invention is realized in an appliance of the kind mentioned in the opening paragraphs in that the transponder according to the invention is present therein. The integration of the IC in the transponder according to the invention and the use of the same dielectric layers as a substrate and as a protective layer mean that the transponder has a smaller thickness and a lower weight than the known transponder. As a result, the appliance can contain a transponder which can be well integrated in a simple manner. Examples of appliances are inter alia paper money and other valuable papers, packagings, toys, clothing, and domestic appliances. A first advantage of the appliance according to the invention is that it is identifiable, while the identification member has a flexible shape. A second advantage is that the transponder is inexpensive. A third advantage, particularly valid when organic materials are used in the transponder, is that there are no materials present which are unsuitable for combustion in refuse incinerators.